The present invention relates to polypeptides which can be used especially in the preparation of immunogens and the obtainment of vaccine against respiratory syncytial virus (RSV) and to nucleotide sequences enabling them to be obtained. The invention likewise relates to an immune adjuvant protein extracted from Klebsiella pneumoniae, to compositions comprising the immunogenic polypeptides, possibly associated with such an adjuvant protein, and to their preparation process.
Respiratory syncytial virus (RSV) is the most frequent cause of respiratory illnesses in the newborn: bronchopneumopathies (bronchiolites). The WHO estimates each year 50 million cases of RSV attacks, from which 160,000 die in the entire world. There are two subgroups of the virus (subgroups A and B).
RSV is classified in the Paramyxoviridae family, a type of pneumovirus comprising a nonsegmented RNA genome, of negative polarity, coding for 10 specific proteins.
There is at present no vaccine available against RSV. Inactivated virus vaccines have been shown to be inefficaceous and have sometimes even aggravated the infections of nursing infants. In the 60""s, vaccination attempts with formalin-inactivated RSV resulted in failure: instead of conferring protection at the time of reinfection due to RSV, the vaccine had the effect of aggravating the illness in the child.
The Application WO 87/04185 proposed to use structural proteins of RSV with a view to a vaccine, such as the envelops proteins called protein F (fusion protein) or protein G, a 22 Kd glycoprotein, a 9.5 Kd protein, or the major capsid protein (protein N).
The Application WO 89/02935 describes the protective properties of the entire protein F of RSV, possibly modified in monomeric or deacetylated form.
A series of fragments of protein F have been cloned with a view to investigating their neutralizing properties.
However, the immune vaccines tested to date have been shown to be inefficaceous or have induced a pulmonary pathology (bronchiolitis or peribronchitis).
At the present time, there is no in-depth treatment of infections due to RSV.
Infections due to RSV of the upper airways: treatment relies essentially on symptomatic medications identical to those for other viral infections.
Infections due to RSV of the lower airways: treatment in nursing infants relies on the maintenance of correct hydration, the aspiration of the secretions and the administration of oxygen if necessary. A positive effect has been observed with ribavirin, a nucleotide which is active in vitro against RSV.
It is for these reasons that an object of the present invention is a polypeptide which is useful especially in immunogen production, characterized in that it is carried by the peptide sequence between the amino acid residues 130 and 230 of the sequence of respiratory syncytial virus protein G, or by a sequence having at least 80% homology with said peptide sequence. This sequence differs slightly for the subgroups A and B of human RSV, or for bovine RSV. The invention comprises the sequences originating from human RSV subgroup A and B, or bovine RSV.
Protein G is an RSV envelope glycoprotein, of molecular weight of between 84 and 90 Kd, which is low in methionine.
The Applicant has demonstrated that the sequence between amino acids 130 and 230 of natural protein G is particularly appropriate for inducing an efficaceous protection against infection by RSV. The invention comprises the sequences originating from human RSV subgroup A or B, or bovine RSV.
More particularly, the present invention relates to polypeptides, which are useful especially as immunogenic element included in the above and which comprise the peptide sequence between the amino acid residues numbered 174 and 187 of RSV protein G (human, subgroups A and B, or bovine) or a sequence having at least 80% homology with the corresponding sequence.
Other peptide sequences adapted to the preparation of an immunogen included in said sequence of RSV protein G are formed by the sequence between the amino acid residues numbered 171 and 187 of human or bovine RSV protein G, or a sequence having at least 80% homology with the corresponding sequence. Other peptides of interest according to the present invention are carried by the sequence between the nucleotides numbered 158 and 190 of RSV protein G or a sequence having at least 80% homology with the corresponding sequence.
According to another method of carrying it out, the invention relates to peptides useful for the preparation of an immunogen and which have a sequence corresponding to the sequence between the amino acid residues numbered 140 and 200 of human or bovine RSV protein G, or a sequence having at least 80% homology with the corresponding sequence. Sequences starting with amino acid 140 of said RSV protein G and whose C-terminal end corresponds respectively to the amino acid 198, 196, 194, 192 or 190, as well as sequences having at least 80% homology with the sequence carried by these fragments, are particularly advantageous.
Among the variants of the above sequences, polypeptides may be mentioned which comprise a sequence in which:
a) the Cys amino acid in positions 173 and/or 186 has been replaced by an amino acid not forming a disulfide bridge, in particular serine, and/or
b) the amino acids in positions 176 and 182 are capable of forming a covalent bridge other than a disulfide bridge, especially aspartic acid and ornithine.
Thus the polypeptide sequence 130-230 of RSV subgroup A can be used complete, in its native form. This sequence corresponds to the written sequence Seq id No. 1 (or G2A).
In the same way, it is possible to use the complete polypeptide sequence 130-230 of RSV subgroup B in its native form. This sequence corresponds to the written sequence Seq id No. 2 (G2B).
The sequence id No. 1 will be written G2A in the remainder of the application.
The sequence id No. 2 will be written G2B in the remainder of the application.
Sequences having at least 80% homology with G2A or G2B are also appropriate.
The sequence between the amino acids 130 and 230 can be modified by the replacement of the cysteine residue in positions 173 and 186 by serine residues to obtain a peptide retaining good immunogenic properties, owing to maintenance of the loop formed by the Cys residues in positions 176 and 182. The amino acid and nucleotide sequences of this polypeptide for subgroup A are represented in seq id No. 3 (G2Axcex4Cys).
For subgroup B, the amino acid and nucleotide sequences are represented in seq id No. 4 (G2Bxcex4Cys).
The peptide sequences will be written G2Axcex4Cys and G2Bxcex4Cys.
According to another aspect, an object of the invention is a polypeptide which is useful for the preparation of immunogen, characterized in that it consists in the peptide sequence between the amino acid residues numbered 174 and 187 of RSV protein G or a sequence having at least 80% homology with said peptide sequence.
In this last sequence the peptide 174-187 subgroup A can have the sequence:
The peptide 174-187 subgroup B can have the sequence:
Th Cys residue in position 186 can also be replaced by a serine residue, so as to obtain the following sequence:
In the sequence between residues 174 and 187 of the immunogenic peptide, according to one of the variants of the invention, the amino acid residues in positions 176 and 182 are respectively replaced by an aspartic acid and an ornithine, so as to obtain one of the following sequences:
The maintenance of the immunogenic properties is obtained owing to the replacement of the disulfide bridge (between the natural Cys residues) by an amide bridge between the positions 176 and 182.
Other sequences according to the invention such as defined above appear in the annex of the present application under the names SEQ ID No. 14 to SEQ ID No. 73.
An object of the invention is likewise a polypeptide which can be used as an immunogenic agent having one of the preceding sequences and which additionally comprises at least one cysteine residue in the N-terminal or C-terminal position.
The invention likewise comprises a polypeptide which consists of the peptide sequence between the amino acid residues numbered 130 and 230 of the RSV protein G sequence subgroup A and subgroup B, or of a sequence having 88% homology with said peptide sequence and which is in the form of a fusion protein with the receptor of human serum albumin, called BBG2Axcex4C or BBG2Bxcex4C, or another linking protein. The sequence of the complete BB protein appears in the annex (Seq ID No. 74).
The invention likewise comprises the variants, for example glycosylated or sulfated, of the different peptides, whether these functions are natural or not.
The polypeptides can be prepared by peptide synthesis or by recombinant DNA techniques, which are known to the person skilled in the art.
In particular, the gene sequences coding for the epitope of approximately 100 amino acids can be prepared by solid-phase assembly of genes, and the corresponding protein expressed, for example, in E. coli by the intracellular route.
The nucleotide sequences (RNA or DNA) coding for the proteins or the polypeptides defined above are part of the invention.
Another object of the invention is an immunogenic agent which comprises a polypeptide such as defined above coupled to a carrier protein, in particular to an immune adjuvant protein.
Preferably, the polypeptide according to the invention is coupled to a carrier protein of the type OmpA of the external membrane of a bacterium of the genus Klebsiella, preferably in the form of a soluble conjugate.
The Applicant has been able to show that although the variants of the sequence 174-187 of the RSV protein G are weakly immunogenic, their coupling with such a protein induces a specific immune response.
The intensity of the immune response has been compared to that obtained with conventional adjuvants, such as coupling to the carrier KLH (keyhole limpet hemocyanin) coadministered with Freund""s adjuvant, or coupling to the carrier protein TT (tetanus toxoid).
Particularly advantageous results are obtained for compositions comprising an immunogenic polypeptide according to the invention coupled to protein p40 of Klebsiella pneumoniae or a protein having 80% homology with protein p40.
More particularly, said polypeptide is coupled to a protein comprising the peptide sequence written Seq id No. 13.
The nucleotide sequence (DNA or RNA) coding for the protein comprising the sequence id No. 13 is comprised in the invention.
The immunogenic polypeptide can be coupled to the immune adjuvant protein by methods known to the person skilled in the art, such as:
Glutaraldehyde
Carbodiimide (e.g.: EDC: 1-(3dimethylaminopropyl)-3-ethylcarbodiimide).
Bis imido esters (e.g.: dimethyl adipimidate).
N-hydroxysuccinimidyl esters (e.g.: disuccinimidyl suberate).
For peptides comprising a supplementary cysteine in the N terminal or C terminal position:
Maleimido-N-hydroxysuccinimide esters (e.g.: MBS: maleimido benzoyl-N-hydroxysuccinimide ester).
N-succinimidyl bromoacetate.
The polypeptide can be conjugated to the carrier protein by a linking protein, for example the human serum albumin receptor (BB).
According to another aspect, an object of the invention is likewise a process for the preparation of a conjugated peptide inserted in a composition useful for prevention or treatment of infections with RSV, characterized in that:
a) the membrane lipopolysaccharides of bacteria of the genus Klebsiella are precipitated in the presence of a salt of a divalent cation and of detergents to recover the total membrane proteins in the supernatant,
b) the proteins are submitted to anion-exchange chromatography to separate the fraction containing the immune adjuvant protein,
c) the fraction containing the immune adjuvant protein is concentrated,
d) the immune adjuvant protein is conjugated with an immunogenic polypeptide such as defined above to form a soluble conjugate.
The divalent cation salt used in step a) is preferably a salt of calcium or of magnesium. After centrifugation, the proteins of the supernatant can be recovered in good yield by two precipitations with ethanol.
The membrane proteins, after resuspension, are separated on an anion-exchange column which can be used under industrial conditions. This chromatographic support is very stable and compatible with drastic pyrogen removal treatments, which was not the case with the chromatographic supports already described. On the other hand, elution of the protein can be carried out under isocratic conditions and not by application of an NaCl gradient (as described previously), which is particularly advantageous under industrial conditions.
According to a preferred method of carrying out the invention, step c) is followed by a second chromatography step, on a cation exchanger, and the fractions containing the adjuvant protein are recovered and concentrated. This supplementary step allows a better elimination of the lipopolysaccharides. The adjuvant protein is then conjugated to an immunogenic polypeptide according to the invention.
According to another aspect, the invention relates to a composition useful for the prevention and/or treatment of infections provoked by RSV, characterized in that it contains a polypeptide characterized above.
More particularly, the compositions additionally contain pharmaceutically acceptable excipients adapted for administration by the injectable route.
In fact, the Applicant has demonstrated that the injection of such compositions affords protection, not by a neutralizing effect, but by a systemic immune response of the body.
The humoral and cellular responses (IgM, IgG, IgA and T cells) are provoked by the product which likewise induces a long-term protection and an immunological memory against the RSV subgroups a and b.
With a view to the administration of the vaccine compositions by the subcutaneous route, it is desirable to have available soluble conjugate, which is difficult by the conventional methods.
It is for this reason that the invention likewise relates to a process for the preparation of a conjugate between an immunogenic peptide and a membrane protein of Klebsiella, in particular the protein p40 of K. pneumoniae, in which the coupling is carried out in the presence of glutaraldehyde at concentrations lower than or equal to 0.05%.
This coupling process considerably reduces the concentrations of glutaraldehyde in comparison with those usually used (2 times 0.01% instead of 1% approximately); the glutaraldehyde is added in 2 portions over a period of five days although the protocols described mention times of 24 hours.
These modifications have allowed the obtainment of a soluble conjugate, in a form adapted for subcutaneous administration.
The usual protocols (higher concentrations of glutaraldehyde and short times) are manifested by the formation of a thick gel (due to P40xe2x80x94P40 conjugation reactions, very probably), a form unfit for administration and manipulation in general.
The conjugated peptide can be frozen and used as such or lyophilized.
The examples which follow are intended to illustrate the invention without in any way limiting the range thereof.